1.
n. [Geology, Shale Gas]
A
fine-grained, fissile, detrital sedimentary
rock formed by
consolidation of clay- and
silt-sized particles into thin, relatively impermeable layers. It is the most abundant sedimentary rock. Shale can include relatively large amounts of organic material compared with other
rock types and thus has potential to become a rich
hydrocarbon source rock, even though a typical shale contains just 1% organic matter. Its typical fine grain size and lack of
permeability, a consequence of the alignment of its platy or flaky grains, allow shale to form a good cap rock for hydrocarbon traps.
Gas shows from shales during drilling have led some shales to be targeted as potential gas reservoirs. Various clay types and volumes influence the quality of the
reservoir from a petrophysical and geomechanical perspective. The quality of shale reservoirs depends on their thickness and extent, organic content,
thermal maturity, depth and
pressure, fluid saturations, and permeability, among other factors.